Redundant Array of Independent Disks (RAID) is a disk group consisting of a plurality of independent disks, which provides larger storage space and more reliable performance than a single disk. In order to recover data when a disk fails, one (for example in RAID3 or RAIDS) or more (for example in RAID6) parity disks are provided in the RAID. However, the reliability of the RAID can be degraded greatly when one or more disks fail in the RAID.
Generally, if one disk in the RAID fails, RAID enters into a degraded mode and utilizes a spare disk to rebuild the RAID. However, since each disk has a limited band width and limited input/output operations per second (IOPS) and the disk capacity is usually high (for example 2T or 4T). Thus, it often causes a time ranging from several days to several weeks for rebuilding the RAID, which makes it very hard to meet high reliability demand.